Wastegate opens too early

Dear fellow Rotax owner,

First a short intro to put things in perspective.

I have an experimental Europa with a 914 turbo, did not build it myself. From day one, I was not overly impressed with the boost performance. For example, I never reached 5800 rpm, even I barely reach 5000 rpm on takeoff.

But it was always good enough to have a good time. Without comparising, I got used to it and never thought much about it. Yesterday I accidentally met someone at the airport with the same aircraft and configuration, and to my surprise he had rocket power on takeoff that blew me away.

Long story short.
I never get more than 31 map on takeoff and never more than 5000 rpm on takeoff (never more than 5300 rpm during cruise and max. 32 map).

Yesterday I pulled my circuit breaker from the TCU (on purpose because then the wastgate would remain in the closed position) to see if I could get a boost past the 31 map with full power, to my surprise I got to 40 map easily and easily to 5500 rpm, and hadn't even reached full throttle yet.

Anyone have any suggestions what and how I should fix the TCU starting to open the wastgate only at 40 map and not already at 32 map?
I have checked my wastegate cable for correct tension and irregularities and this appears to be OK (it proved to be closed with the TCU turned off).

Unfortunately I have the first series of the TCU and there is no shop in the area that can read it, because of the old software and dongle you need.
Could there be things other than the TCU that could be causing this? For example the pressure sensors?

Thank you in advance if you have any ideas you would like to share.

Kind Regards, Renz

P.s. I read the forum threads related to this, but look for some different perspectives.